The present invention relates to a glass-sealed semiconductor device.
A conventional glass-sealed semiconductor device has the following structure, as shown in FIGS. 4A and 4B. Low-melting glass 3 is glazed in the entire region which surrounds a central recess 1 in a ceramic base 2, and a lead frame 4 for extracting external electrodes is fixed on the low-melting glass 3. Frame electrodes 5 for wire bonding having an aluminum layer thereon are formed at distal ends of the lead frame 4. A semiconductor element 6 is fixed to the recess 1 by a metal grazing material or the like, and electrode pads of the semiconductor element 6 and the frame electrodes 5 are electrically connected through metal wires 7. The low-melting glass 3 has a small three-dimensional surface pattern, thus constituting a glossy structure.
Wire bonding of the conventional glass-sealed semiconductor device is performed as follows. At the time of wire bonding, the lead frame 4 has an outer frame 12, as shown in FIG. 5. Holes 13 are formed at predetermined positions of the outer frame 12.
In order to wire-bond a semiconductor element 6, pad coordinates (X.sub.p, Y.sub.p) of the semiconductor element 6 and coordinates (X.sub.l,Y.sub.l) of the frame electrodes 5 at a reference position are stored in a bonder. On the pad side, the position of the semiconductor element 6 is automatically detected by pattern recognition prior to bonding, and differences (.DELTA.X.sub.p, .DELTA.Y.sub.p, and .DELTA..theta..sub.p) (where .DELTA..theta..sub.p represents an angular difference) between the detected positions and the reference position are calculated. The reference coordinates (X.sub.p, Y.sub.p) are corrected and calculated, thereby starting bonding.
On the side of the frame electrodes 5, positioning pins are respectively fitted in the holes 13 formed at the predetermined positions of the outer frame 12 on a bonding stage. The actual position of each frame electrode 5 is caused to coincide with the reference coordinates, and bonding is performed without correcting the reference coordinates (X.sub.l,Y.sub.l). Errors tend to occur in bonding on the side of the frame electrodes 5. Bonding precision on the side of the frame electrodes 5 is poorer than that on the pad side because a positional relationship between the frame electrodes 5 and the holes 13 is lost due to patterning errors of the lead frame 4 and a mounting error of the lead frame 4 on the ceramic base 2. In addition, misalignment between the diameter of the positioning pin and the diameter of the corresponding hole 13 also causes the above error.
In order to improve bonding precision on the side of the frame electrodes 5, the actual position of the frame electrode 5 is automatically detected by pattern recognition on the side of the frame electrodes 5. However, since the low-melting glass 3 has a glossy surface due to a small three-dimensional surface pattern and reflects light, light reflected by the glass surface is mixed in a video signal from the frame electrode 5. The actual position of this frame electrode 5 cannot be pattern-recognized. For example, if the above light reflection does not occur, a binary image is obtained wherein a glass portion is given as black (i.e., a hatched portion) and a frame electrode is given as white in FIG. 3A. When light is reflected by the glass surface, it is given as white, as shown in FIG. 3B. The shape of the frame electrode 5 becomes unclear, and pattern recognition cannot be performed.
As described above, when the frame electrodes in the conventional glass-sealed semiconductor device are to be bonded, bonding errors occur, and reliability of connections between metal wires and the frame electrodes is degraded.